With regard to vehicles in general, and at least to some extent heavy/commercial vehicles such as trucks, buses and the like, there is constantly ongoing research and development with regard to increasing fuel efficiency and reducing exhaust emissions.
This is often at least partly due to growing governmental concern in pollution and air quality, e.g. in urban areas, which has also led to the adoption of various emission standards and rules in many jurisdictions.
These emission standards often consist of requirements that define acceptable limits for exhaust emissions of vehicles being provided with internal combustion engines. For example, the exhaust levels of e.g. nitric oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) and particles are regulated for most kinds of vehicles in these standards.
The undesired emission of substances can be reduced by reducing fuel consumption and/or through the use of aftertreatment (purifying) of the exhaust gases that results from the combustion process.
Exhaust gases from the internal combustion engine can, for example, be treated through the use of a so-called catalytic process. There exist various kinds of catalytic converters, where different types can be used for different kinds of fuel and/or for treatment of different kinds of substances occurring in the exhaust gas stream. With regard to at least nitric oxides NOx (such as, for example, nitric oxide NO and nitric dioxide NO2, respectively) heavy vehicles often comprises a method where an additive is supplied to the exhaust gas stream. The additive is supplied in order to, usually through the use of a catalytic converter, reduce the presence of nitric oxides NOx to less pollutive substances (mainly nitrogen and water vapor). The additive can be injected in the exhaust gas stream resulting from combustion in the internal combustion engine upstream the catalytic converter, and one common type of catalytic converter that is used in NOx reduction of this kind is Selective Catalytic Reduction (SCR) catalytic converters.
In the supplying of an additive it is essential that the amount of additive that is supplied to the exhaust gas stream is neither too great nor too small. Consequently, it is desirable that the supplied amount of additive corresponds to an expected amount of additive.